1. Field of the Invention
The present invention relates to a display device including a light emitting element and to a driving method thereof, and particularly to a display device including a light emitting element, which is controlled by current, and to a driving method thereof.
2. Description of the Related Art
Display devices including light emitting elements have been developed. For example, a display device including a plurality of pixels each having a light emitting element and a drive transistor electrically connected to the light emitting element have been developed. In such a display device, the luminance of each pixel is controlled by controlling the amount of current flowing through a light emitting element with the use of a drive transistor.
The threshold voltage (hereinafter referred to as Vth) of a drive transistor, however, might vary between pixels. For this reason, a threshold voltage compensating pixel circuit, which compensates variations in Vth of a drive transistor, has been researched. A display device with a threshold voltage compensating pixel circuit in which a drive transistor is a diode-connected transistor has been researched, for example (see Patent Document 1).
A pixel circuit described in Patent Document 1 has a drive transistor Q1 which is a diode-connected transistor whose gate and source are connected to each other. Moreover, the pixel circuit includes a capacitor C2, a signal line Ui, and a signal line Sj. A gate of the drive transistor Q1 is electrically connected to one terminal of the capacitor C2; the other terminal of the capacitor C2 is electrically connected to the signal line Ui; and a drain of the drive transistor Q1 is electrically connected to the signal line Sj. The display device having the pixel circuit described in Patent Document 1 is capable of changing the potential of the signal line Ui in three levels, and capable of compensating Vth of the drive transistor Q1 by changing the potential of the other terminal of the capacitor C2 while applying a predetermined potential to the drain of the drive transistor Q1.